The present invention relates to a thermal recording device, and particularly to a method of forming a distributing wire for the thermal recording device.
Generally the thermal recording device is used for recording in formation by thermal recording or a thermal transcribing method. The thermal recording device is comprised of a plurality of heat-generating resistance, formed on a ceramic insulating substrate (on which a glaze is spread), and the heat-generating resistances are electrically connected to a driving integrated circuit in order to enable performance of each of the heat-generating resistance;
Thus if processed digital pulses are applied to the respective bits of the driving integrated circuit, the respective bits perform switching operations independently, so that the respective heat-generating resistances are driven. As a result, the heat generated from the heat-generating resistances are transferred to a heat-sensitive paper to enable a printing operation.
Referring to FIG. 1 which illustrates a partial plain view of a conventional thermal recording device, the conventional thermal recording device comprises a plurality of heat-generating resistances 10, a first wiring 12, first and second bonding pads 16, 17, and a second wiring 22. The wiring 12 formed on a heat-generating resistance film (not shown in the drawing) is extended in the vertical direction, i.e., in a first direction adjacently to the heat-generating resistances 10, and arranged in parallel in the horizontal direction, i.e., in a second direction. The first and second bonding pads 16, 17 are electrically connected to a driving integrated circuit via the first the wiring 12. The second wiring 22 is disposed between the first and second bonding pads 16, 17.
The region 1 consisted of the heat-generating resistances 10, the wiring 12 and the first bonding pad 16 is a region formed by applying a thin film manufacturing process, while the region 2 consists of the second bonding pad 17 is a driving integrated circuit region.
Referring to FIG. 2, a cross-sectional view of a preferred embodiment of a conventional thermal recording device, vertically taken along the line A--A' of FIG. 1, is shown. It is noted that the parts same as those of FIG. 1 are assigned with the same reference numbers.
Referring to FIG. 2, a sectional view comprises a glaze layer 32 formed on a ceramic substrate 30 which is containing aluminum oxide (Al.sub.2 O.sub.3) as the main ingredient, a heat-generating resistance film 10a formed on the glaze layer 32 except a part thereof, a wiring 12 formed on the heat-generating resistance film 10a except the predetermined portion thereof, a common wiring 14 formed on a part of the wiring 12, a protecting film 16 formed on the exposed portion of the heat-generating resistance film 10a and a wiring film 12 adjacently to the film 10a, a solder resist 18 for protecting the wiring 12 not coated with the protecting film 16, a driving integrated circuit 20 stacked on a portion of the glaze layer 32 where the heat-generating resistance film 10a and the wiring 12 are not formed, a wire bonding 22 (gold wire) for electrically connecting the driving integrated circuit 20 to the wiring 12, and first and second resins 24, 26 for protecting the driving integrated circuit 20 and the wire bonding 22. In the above case, the protecting film 16 is made of tantalum oxide (Ta.sub.2 O.sub.5), silicon oxide (SiO.sub.2) or silicon-nitride-oxide (Si-N-O).
Referring to FIG. 3, a sectional view of a vertical direction of FIG. 1, i.e., a sectional view taken along the line A--A' of FIG. 1, showing another form of the conventional device. It is noted that the parts same as those of FIGS. 1 and 2 are assigned with the same reference numbers. The difference between in FIG. 2 and FIG. 3 is that the glaze layer 32a of FIG. 3 formed on the substrate 30 of the same thickness as FIG. 2, is in a semicircular shape The rest of the constitution of FIG. 3 is the same as that of FIG. 2. As shown in FIG. 3, the method of forming the glaze layer 32a is called a "partial glaze forming method". As shown in FIG. 4, the thermal recording device which is manufactured by applying the partial glaze forming process is constituted such that the wiring 12 in the regions adjacent to 10 the exposed heat-generating resistance 54 (lying upon the partial glaze layer 52) is formed with a thinner thickness than that of the rest of the wiring.
In FIGS. 2 and 3, the thickness of the heat-generating resistance is about 0.3 .mu.m, and that of the wiring is 0.5-2 .mu.m. Therefore, there occur incomplete contact portions between the thermal recording paper and the heat-generating resistance due to the height difference existing at the end portion of the wiring. If the thickness of the wiring is reduced in order to overcome this contact defect, then the whole wiring resistance value is increased, and therefore, it is impossible to reduce the thickness of the wiring to below 0.5 .mu.m.
If the thickness of the wiring is reduced, not only the overall resistance value is increased, but also the thickness of a portion of a gold wire for electrically connecting between the components has to be decreased. In order to assure the reliability for the electrical connection, at least 1 .mu.m or more of thickness is required.
As a result, the thickness of the wiring can not be formed in less than 1 .mu.m, and therefore, the height difference between the heat-generating resistance and the wiring becomes more than 1 .mu.m. Thus, due to the height difference between the heat-generating resistance and the wiring, the thermal recording paper is subjected to contact defects, and these contact defects causes energy losses during the operation of the thermal recording device due to the insufficient contact between the thermal recording paper and the heat-generating resistance.